This invention relates to array antennas and, more particularly, to such antennas arranged for operation with sum and difference excitation.
Sum and difference excitation has been provided in monopulse type simultaneous lobing implementations. In such implementations, sum and difference excitation levels have typically been comparable or identical. A result has been that principal sum and difference sidelobe patterns, while differing, have typically been of comparable relative levels or magnitude.
In some usages, such as particular Identification Friend or Foe (IFF) applications, it is desirable that the minimum difference sidelobe level exceed the maximum sum sidelobe level regardless of system implementation variables. Thus, operationally it is desirable that no sum side lobe level exceed a relevant difference side lobe level. The occurrence of a sum sidelobe level exceeding an associated difference sidelobe level in this context may be termed “punch-through.” Typical prior implementations employing similar or identical sum and difference excitations have not been entirely satisfactory for such usage. For example, the capability to improve sum mode gain, while maintaining a desired difference-to-sum sidelobe margin, may be limited.
Accordingly, objects of the present invention are to provide new and improved array antennas and such antennas which may have one or more of the following characteristics or capabilities:                operation with sum and difference patterns;        independent sum and difference excitation level capability;        difference excitation adjustment to increase difference sidelobe level;        relative adjustment of sum and difference excitation levels and resulting sidelobe levels;        sum mode gain increasable, while meeting difference-to-sum sidelobe margin objective;        adjustment to cause minimum difference sidelobe level to significantly exceed maximum sum sidelobe level;        improved punch-through performance; and        low-complexity implementation.        